In a cellular communication technology, a base station manages one or more communication areas, and performs radio communications with a communication terminal within the communication area. The communication area is called “cell”, and the same radio band is generally used within one cell. Therefore, in a case where the communication terminal performs communications by using the same radio resource as that of an adjacent cell thereto, the communication terminal receives strong interference (hereinafter, referred to as “adjacent-cell interference”) from the adjacent cell.
For example, in an uplink, in a case where communication terminals in a vicinity of a cell boundary with respect to the adjacent cell simultaneously perform transmission by using the same radio resource, a level difference between a desired signal and the adjacent-cell interference is small, which leads to a problem that communication quality greatly deteriorates. Similarly in a downlink, assuming that, for example, transmission power of the respective cells are constant, the terminal in the vicinity of the cell boundary has a small level difference between the desired signal received by the terminal and the adjacent-cell interference, which leads to a problem that the communication quality greatly deteriorates. Further, in the radio communications, shadowing that causes a radio wave strength to vary occurs also due to a radio wave covered or reflected by a building or the like, and hence from the viewpoint of the adjacent-cell interference, a cell that is not geographically adjacent can be the adjacent cell.
For example, in a next-generation high-speed mobile communication technology (long term evolution (LTE)) defined by a standardization project for a third-generation mobile communication system (3rd Generation Partnership Project (3GPP)), application of inter-cell interference coordination (ICIC) is expected as a technology for solving the problem of the adjacent-cell interference (Non Patent Literature 1). ICIC has an object to control inter-adjacent-cell interference, and describes that it is necessary to consider information obtained from another cell, such as a resource usage status, a traffic load, and the like. Further, as one of a method of implementing ICIC, there is a frequency reuse (fractional frequency reuse (FFR)) technology. In FFR, separate priority bands are set for the respective cells.
The base station uses communication quality information reported from a communication terminal to determine whether the communication terminal is a communication terminal subjected to a weak influence of the adjacent-cell interference (hereinafter, referred to as “center terminal”) or a communication terminal subjected to a strong influence of the adjacent-cell interference (hereinafter, referred to as “edge terminal”). Then, restriction of a usable band is avoided when the communication terminal is determined as the center terminal, while the usable band is restricted to the priority band for a local cell when the communication terminal is determined as the edge terminal. A scheduler allocates radio resources based on channel quality from among bands that can be used by respective communication terminals (Non Patent Literature 2).
Note that, as a method of causing base stations to notify each other of priority bands, LOAD INFORMATION is specified (Non Patent Literature 3). The notification through the uplink is enabled by high interference indication (HII), and the notification through the downlink is enabled by relative narrowband Tx power (RNTP).